Xbox on Windows 8 Won't Sell 'Mature' Titles

[UPDATE] As pointed out in the comments, the wording of the requirements implies that MATURE titles will be allowed in the store, though PEGI 18+ titles will not.
[ORIGINAL]
Microsoft has gotten tons of criticism for Windows 8. Much of the criticism has focused on the operating system's tile-based user interface, but a significant amount has also focused on Microsoft's inclusion of a game store built-in to the OS.

Valve's Gabe Newell criticized the game store because it could limit the access indie game developers have to the PC platform and make games in the game store seem more "official" than others. Valve's own game store, Steam, recently launched a voting mechanism that allows users to choose what indie games are sold in the Steam Store.

Today gamers have another reason to criticize the Windows 8 game store, which is rumored to be Xbox-branded. Rock, Paper, Shotgun this week pointed out that the Windows 8 app certification requirements require Windows Store apps to be under a MATURE or PEGI 18+ rating. From the requirements document:

Apps with a rating over PEGI 16, ESRB MATURE, or that contain content that would warrant such a rating, are not allowed. Metadata and other content you submit to accompany your app may contain only content that would merit a rating of PEGI 12, ESRB EVERYONE, or Windows Store 12+, or lower.

It seems Steam might not have much to fear from the closed-off Microsoft Store. By shunning blockbuster MATURE-rated titles such as Assassin's Creed III, Skyrim, and Resident Evil 6, and by making certification a barrier to entry, Microsoft is effectively leaving out a good portion of the PC gaming market.

By going after the casual market, Microsoft has taken steps to ensure that their video game store on Windows 8 will be quite irrelevant to many PC gamers. That could be the plan, though. It would certainly leave the PC gaming market more open, comforting many developers that have their own platforms.